Regional climate affects salmon lice dynamics, stage structure, and management

Abstract

Regional variation in climate can generate differences in population dynamics and stage structure. Where regional differences exist, the best approach to pest management may be region specific. Salmon lice are a stage structured marine copepod that parasitizes salmonids at aquaculture sites worldwide, and have fecundity, development, and mortality rates that depend on temperature and salinity. We show that in Atlantic Canada and Norway, where the oceans are relatively cold, salmon lice abundance decreases during the winter months, but ultimately increases from year-to-year, while in Ireland and Chile, where the oceans are warmer, the population size grows monotonically without any seasonal declines. In colder regions, during the winter the stage structure is dominated by the adult stage, which is in contrast to warmer regions where all stages are abundant year round. These differences translate into region specific recommendations for management: regions with slower population growth have lower critical stocking densities, and regions with cold winters have a seasonal dependence in the timing of follow-up chemotherapeutic treatments. Predictions of our salmon lice model agree with empirical data, and our approach provides a method to understand the effects of regional differences in climate on salmon lice dynamics and management.

Regional climate affects salmon lice dynamics, stage structure and management

“…To calculate the follow-up treatment window when the simplifying assumption is relaxed to allow for seasonality, whereby past temperatures can be warmer or cooler than the current temperature, we calculate the values of t P (t) and t C (t), which are the lengths of time spent in the nauplius and chalimus/ pre-adult stages for a salmon louse that exits these stages at time t. We numerically solve equations (2.2), and we again assume that the time spent in the copepodid stage is 10 days (see electronic supplementary material, §S5). Complete details of our numerical methods are provided in electronic supplementary material, § §S4 and S5, and all code to produce our results is publicly available in Hurford et al [34].…”

“…All the data contained in this manuscript has been previously published elsewhere. Files containing these published data are archived alongside the code files [34]. Dataset available as part of the electronic supplementary material.…”